Multi-layer golf balls contain a core, which may include one or more layers of solid material or one or more layers of solid material encompassing a fluid therein, and a cover. Optionally, an elastic winding may also be used to form a layer surrounding the center to provide certain playing characteristics. Such balls are known as “wound” balls. The multi-layer golf balls discussed herein include a core and a cover. The terms “core” or “ball core,” as used herein, include a center having one or more layers and an intermediate layer formed of one or more layers. The terms “center” or “ball center,” as used herein, include a solid and/or fluid mass around which an intermediate layer and a cover are disposed. The intermediate layer is disposed between the center and the cover, typically in concentric fashion, with the cover being the outermost portion of the ball.
A variety of golf ball compositions are known and used in various methods of manufacture. Unfortunately, these compositions and methods tend to produce balls that do not consistently achieve a symmetrical core. See, for example, the discussion in U.S. Pat. No. 6,056,842, which illustrates the poor centering that occurs in conventionally formed golf balls. Multi-layer ball production has been plagued by center portions that become off-centered during the manufacture of such balls. Off-center golf balls are a hindrance to many players, particularly those able to achieve great control using a symmetrical ball. This lack of symmetry is now believed to be caused, at least in part, by the materials and methods conventionally used in forming multi-layer golf balls. Compositions typically including greater than 40 percent cis-1,4-polybutadiene isomer are often used in forming golf ball cores, or a portion thereof. Unfortunately, many cis-polybutadiene materials are fairly soft prior to crosslinking, which can lead to the off-centering problems noted above. A number of references disclosing various cis-polybutadiene materials are discussed below.
U.S. Pat. Nos. 3,896,102; 3,926,933; 4,020,007; and 4,020,008 disclose a 1,3-butadiene component and a method and catalyst for preparing trans-polybutadiene, and that it is well known that increasing content of trans-polybutadiene is more resinous and produces a more elastic, tough, crystalline, thermoplastic solid. The '933 and '008 patents further disclose that trans-polybutadiene is resistant to attack by ozone and other chemical agents, and is typically used in insulation, battery cases, and golf ball covers.
U.S. Pat. No. 4,020,115 discloses the preparation of homopolymers and random copolymers of butadiene with styrene and/or isoprene that include butadiene units having a low vinyl content of not over 12 percent and a trans-polybutadiene structure of from about 70 to 81 percent. These polymers are disclosed to have broad molecular weight distribution, as well as tack and green-strength desired for manufacturing tires. A variety of trans-polybutadiene and vinyl-polybutadiene materials are also disclosed with the catalysts used for the preparation thereof.
U.S. Pat. No. 4,919,434 discloses a two-piece golf ball having a solid core of more than 40% cis-1,4-polybutadiene isomer and a cover having an inner layer of 0.1 to 2 mm thickness and an outer layer of 0.1 to 1.5 mm thickness. The inner layer is a thermoplastic resin, such as an ionomer, polyester elastomer, polyamide elastomer, thermoplastic urethane elastomer, propylene-butadiene copolymer, 1,2-polybutadiene, polybutene-1, and styrene-butadiene block copolymer, either individually or in combination.
U.S. Pat. No. 4,929,678 discloses a rubber composition for golf balls including at least 40 percent by weight polybutadiene rubber with a Mooney viscosity of 45 to 90 and a cis-bond content of at least 80 percent, a co-crosslinking agent, and a peroxide. These polymers are disclosed to have a dispersity of between 4.0 to 8.0, which is a ratio of weight average molecular weight to number average molecular weight.
U.S. Pat. No. 4,931,376 discloses butadiene polymers and copolymers with another conjugated diene having at least 80 percent butadiene by weight; 60 to 98 percent trans-polybutadiene linkages; a molecular weight distribution of 1.1 to 4.0; melting temperature of 40° C. to 130°C.; and a content of insolubles in boiling cyclohexane of 1% or less, as well as processes for making the same. Weight average molecular weights of 30,000 to 300,000 and trans-polybutadiene contents greater than about 30 percent are preferred. These materials are disclosed for use in golf ball covers, splint or gyps material, and the like.
U.S. Pat. No. 4,955,613 discloses golf balls made from two polybutadienes, each having a Mooney viscosity below about 50 and a cis-polybutadiene isomer content of greater than about 40 percent, more preferably greater than about 90 percent, and catalysts for preparing the polybutadienes.
U.S. Pat. No. 4,971,329 discloses solid golf balls made from polybutadiene mixtures of about 99.5 to 95 weight percent cis-1,4-polybutadiene and about 0.5 to 5 weight percent vinyl-1,2-polybutadiene. The cis-polybutadiene is made by blending from about 80 percent to 100 percent by weight of cis-polybutadiene with a cis-content of 95 percent and about 0 weight percent to 20 weight percent of cis-polybutadiene with a cis-content of about 98 percent.
U.S. Pat. No. 5,553,852 discloses three-piece solid golf balls having a center core, intermediate layer, and cover. The center core is prepared with a 1,4-polybutadiene containing more than 90% cis-polybutadiene isomer for high repulsion, co-crosslinking agent(s), peroxide, and other additives.
U.S. Pat. No. 5,833,553 discloses core compositions including polybutadiene, natural rubber, metallocene catalyzed polyolefins, polyurethanes, and other thermoplastic or thermoset elastomers, and mixtures thereof having a broad molecular weight range of 50,000 to 500,000, preferably from 100,000 to 500,000. Polybutadiene with a high cis-content is noted as being preferred.
U.S. Pat. No. 5,861,465 discloses thread rubber for wound golf balls having rubber component obtained by vulcanizing rubber composition including rubber selected from natural rubber, synthetic high-cis-polyisoprene rubber, and mixtures with at least one specific diaryl disulfide, a vulcanizing agent, and an antioxidant.
U.S. Pat. No. 6,018,007 discloses the preparation of trans-polybutadiene and other polymers and copolymers having trans configuration in the conjugated diene monomer contributed units with improved catalyst systems. The resulting polymers are rubbery, except those with high trans content, and may be vulcanized by well known methods and incorporated in tires, general rubber goods, and plastics materials.
U.S. Pat. No. 6,130,295 discloses a two-piece golf ball having an unvulcanized cover that includes a mixture of ionomer and polybutadiene having a trans-isomer content of at least 60 percent.
It is desirable to reduce the off-centering problem and manufacturing inconsistencies found in many conventional golf balls, although little notice has been taken of this important part of golf ball manufacture until recently. In part, many materials are difficult to work with before they have been crosslinked. The polymers typically used in the core, particularly in intermediate layers or shells, tend to have a memory that urges the polymer back to its earlier or original shape, which necessitates rapid compression molding to crosslink the polymer as soon as the shells are formed.
It is also understood that there has been great difficulty in the art when attempting to blend certain polymer materials having different microstructures, e.g., polybutadiene and polyisoprene. Thus, it is desired to find an improved composition and method for providing such composition, for use in manufacturing golf balls that reduces or avoids the disadvantages present when using conventional materials for golf balls.